1. Field of the Invention
This invention relates to a clamping device in which the clamping actuator is operated with pressurized fluid to clamp a workpiece, and more particularly to an electrical device for detecting the clamping conditions of the workpiece from the flow rate of pressurized fluid.
2. Description of the Prior Art
A clamping device of this type is provided at each machining station in a transfer machine to hold a workpiece in place for a machining operation, automatic assembling operation, etc. For this purpose, in general, actuators, such as hydraulic cylinders, are employed.
At the machining station, the machining operation is started after it is confirmed that the workpiece is satisfactorily clamped. Heretofore, the clamping of the workpiece is detected with a dog connected to the piston rod of the hydraulic cylinder and a limit switch provided at the clamping position. However, in the case where it is required to handle workpieces different in size from the previous ones, the mounting position of the limit switch must be changed, and changing the setup accordingly takes a relatively long period of time.
The clamping of the workpiece can be indirectly confirmed by measuring the flow rate of the pressurized fluid. For instance Japanese Patent application Publication No. 35182/1973 has disclosed the technical concept that the length of a multi-stage expansion boom can be represented by the flow rate of the fluid. However, the conventional method merely indicates the length of a multi-stage expansion boom, and cannot be applied to a clamping device as it is. That is, in a clamping device, it is necessary to confirm or detect the kind of a workpiece from the stroke of the actuator, and to confirm the clamping and unclamping of the workpiece to perform the following operations successively.